Hi! I know im a little late but I was wondering what your outcome was with taking it as needed. I am in the same position you were. I hope you get a chance to read this.
Metoprolol come is both slow release and in normal release, the normal release is much lower cost in the USA and is called Metoprolol Tartarait (sp?). I used the slow release once a day for a few years but got approval to move to the regular release taken at 1/2 the former dose rate, but I take it twice a day. I do not suffer from SVT, but I do take BB.
I've received two different instructions from my family physician, and my cardiologist. The former put me on 100mg/day and told me that if I had an SVT event, to chew on one, and that it would help in converting it. When I told my cardiologist, he politely told me that "it doesn't work that way". So take your choice. Regardless, I found Metoprolol ineffective in preventing episodes, which in my case had grown to 3 to 5 times per month. I do think however that the drug helped in converting episodes. I had a self sustaining form of SVT that once initiated, would run on until I intervened or I guess dropped over.
I think it depends on which brand you're using. Some of them are in "slow release" formula (so a dose of say 25 mg is released through 24 hours) and will not work as a "pill in the pocket".
I have a beta blocker for use when needed, but that one is propranolol and not metoprolol (slow release). Propranolol works better towards anxiety, stress and other factors that may trigger a rapid heart rhythm. From time to time (generally stressful times) I can take 12,5 or 25 mg metoprolol in addition.
But I guess this is something that your doctor should decide as we are all different.
I have heard of patients taking i\t on an "as needed" basis. I guess that means your SVT isn't that bad where you need it daily, so that is a good thing.